Expandable silica particles
By coating kaolin and talc powder on the outer surface of expandable silica particles, the risk of adhesion and melting at high temperatures is solved, and the strength and water absorption resistance of the particles are improved, and the physical properties of the material are maintained.
Patent Information
- Application Number
- CN202510361264.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2020-06-04
- Filing Date
- 2021-05-10
- Publication Date
- 2025-06-27
AI Technical Summary
At temperatures close to the plastic-melting state transition, the expanded silica particles are prone to adhere to each other and/or to the furnace, and the risk of internal pore wall rupture and outer surface pore collapse increases, resulting in weakening of material properties and increased water absorption.
Expandable silica particles containing silica powder, fume and expansion agent are used and coated with kaolin and talc powder on their outer surfaces to reduce the risk of adhesion and melting and enhance the elasticity of the particles and the sealing of the pores.
It effectively reduces the risk of expandable silica particles adhesion and melting at high temperatures, reduces the possibility of pore wall rupture and pore collapse, thereby improving the strength and water absorption resistance of the particles and maintaining the physical properties of the material.
Smart Images
Figure CN120208246A_ABST
Abstract
Description
[0001] This application is a divisional application of Chinese Patent Application No. 202180034048.2, with the filing date of May 10, 2021 and the invention title of "Expandable Silica Particles". Technical Field
[0002] The present disclosure relates to expandable silica particles, a method for expanding silica particles, expanded silica particles produced by the method, uses of the expanded silica particles, and a method for producing expandable silica particles. Background Art
[0003] Expanded silica particles are used in various fields, such as as fillers in matrix materials such as concrete or epoxy resins, as insulating materials together with various binder materials, or as water filtration media. Several advantageous physical properties are associated with expanded silica particles, such as low density, high dimensional stability, excellent compressive strength, and high insulating capacity. The expanded silica particles added to the matrix material can also improve the processability of the matrix material before hardening, for example, by improving the fluidity at a very low water absorption rate. Additionally, the expanded silica particles can reduce the overall material cost, especially for expensive matrix materials. Finally, by using post-consumer recycled glass, the expanded silica material contributes to environmental sustainability.
[0004] During the production of expanded silica particles, it is desirable to use the expanded silica particles close to the temperature at which the transition from the plastic state to the molten state occurs. At these temperatures, the material of the expanded silica particles provides the least resistance to the ongoing expansion. Thereby, a more optimal expansion and a more uniform spherical shape of the expanded silica particles are achieved. However, due to the expanded silica particles being close to the transition from the plastic state to the molten state, problems can occur in commonly used methods. Close to this transition, the expanded silica particles are more prone to adhering to each other and to the surrounding furnace in which the particles expand. Although kaolin coatings can be used as release agents, kaolin transforms into metakaolin at temperatures close to the plastic-molten transition temperature and can thereby lose most of its properties as a release agent. Metakaolin can also melt onto the surface of the softened expanded silica particles, further reducing its effect as a release agent.
[0005] In addition, due to the low viscosity at temperatures close to the transition from the plastic state to the molten state, the internal cell walls can rupture, resulting in an open-cell internal structure, while the pores at the outer surface of the expanded silica particles can collapse. When using kaolin coating as a release agent, the surface of the expanded silica particles can become additionally more brittle, leading to a further risk of pore collapse at the outer surface and thus physical property cracking. These effects can result in weakened expanded silica particles and an increased ability of the expanded silica particles to absorb fluids such as water. Especially when used as a filler in a matrix material, such as an organic or inorganic binder, the high absorption ability can cause the expanded silica particles to absorb a large amount of the matrix material. The absorption of such a matrix material negatively affects the properties of the expanded silica particles as a filler material. For example, the absorption of concrete additives such as water reducers and air-entraining agents will have an important impact on the flow behavior and mechanical properties in the cured state. This offsets the desired effect of reducing the overall material density of the matrix and the filler.
[0006] Therefore, there is a clear need for improved expandable silica particles that can expand at temperatures close to the plastic-melt transition, while reducing the risk of softened expandable silica particles adhering to each other and / or to the furnace, and reducing the risk of internal cell wall rupture and pore collapse at the outer surface. Summary of the Invention
[0007] The present disclosure relates to expandable silica particles according to claim 1 and a method for producing expandable silica particles according to claim 8. The present disclosure also relates to a method for producing expanded silica particles according to claim 10, the use of the expanded silica particles according to claim 13, and the use of the expanded silica particles according to claim 14. Brief Description of the Drawings
[0008] Figure 1 Schematically shows a furnace for heating expandable silica particles according to the disclosure. Detailed Description
[0009] The expandable silica particles according to the present disclosure comprise silica powder, silica fume and at least one blowing agent. The expandable silica particles further comprise a coating provided on the outer surface of the expandable silica particles, wherein the coating comprises kaolin powder and talc powder. Advantageously, the kaolin acts as a mold release agent, while the talc counteracts the negative effects of the kaolin at high temperatures by making the outer surface of the expanded silica particles more elastic and having closed pores. Optionally, the expandable silica particles may further comprise other additives such as colorants. The expandable silica particles may have a bulk density of 0.3 - 1.7 kg / l, preferably 0.5 - 1.5 kg / l. The expandable silica particles may have a diameter of 0.1 - 40 mm, preferably 0.25 - 5.6 mm, most preferably 0.8 - 1.6 mm.
[0010] The expandable silica particles comprise 50 - 98% by weight of silica powder. The particles of the silica powder may have a diameter of 0.01 - 700 μm. Preferably, the silica powder comprises recycled glass powder. The recycled glass powder may for example be derived from post - consumer recycled glass, soda - lime glass, float glass, windshields, solar panels. Advantageously, the expandable silica particles thus form an environmentally friendly material.
[0011] The expandable silica particles may comprise 0.85 - 10% by weight of at least one blowing agent. The blowing agent may comprise a powder. Preferably, the particles of the blowing agent powder have a diameter of 0.01 - 40.0 μm. The at least one blowing agent may comprise aluminum nitride (AlN), silicon carbide (SiC), manganese dioxide (MnO2), sodium carbonate (Na3CO3), calcium sodium carbonate (CaNa3CO3) or a combination thereof. Preferably, the at least one blowing agent comprises silicon carbide powder.
[0012] The expandable silica particles may comprise 0.01 - 10% by weight of silica fume. The silica fume comprises ultrafine silica particles having a particle diameter of less than 1 μm. Preferably, the diameter of the silica fume particles is about 150 nm. Advantageously, the silica fume strengthens the pore walls formed in the expandable silica particles during expansion. Thus, the rupture of the pore walls during expansion is reduced. Due to the strengthened pore walls and due to the reduced occurrence of pore wall rupture, the resulting expanded silica particles have higher strength, higher crush resistance and significantly reduced water absorption.
[0013] The coating may comprise 0.5 - 10% by weight of kaolin powder (Al2SiO5(HO)4). Advantageously, the kaolin acts as a mold release agent. Thereby, the risk of the expandable silica particles adhering to each other and / or to the furnace is reduced. This is particularly important for large production volumes where many particles expand simultaneously. However, the endothermic dehydration of kaolin occurs in the temperature range of 560 - 950 °C, producing metakaolin, which will gradually reduce the effect of kaolin as a mold release agent. Therefore, the coating also contains talc powder (Mg3Si4O 10 (OH)2). The coating may comprise 0.5 - 5% by weight of talc powder. Advantageously, during expansion, the talc powder melts into the surface of the expanded silica particles and makes the surface more elastic or flexible, thereby reducing the collapse of pores at the outer surface of the expanded silica particles. Thus, the talc powder counteracts the adverse effects of kaolin occurring at high temperatures and serves to maintain the surface integrity of the expanded silica particles. Thereby, the fluid absorption resistance in the expanded silica particles is improved.
[0014] Next, a method for preparing one or more expandable silica particles according to the present disclosure is described. The method includes providing expandable silica pre-particles comprising silica powder, silica fume, and at least one blowing agent. Providing the expandable silica pre-particles may include sintering or hot-pressing a mixture of silica powder, silica fume, and at least one blowing agent into a block at a temperature below the activation temperature of at least one blowing agent. Then, the block may be divided into expandable silica pre-particles, for example, by cutting or by crushing the sintered block into pellets. The pellets may be filtered according to size and the large pellets may undergo further separation. Alternatively, the mixture of silica powder, silica fume, and at least one blowing agent may be directly hot-pressed into expandable silica pre-particles. Additionally alternatively, the mixture of silica powder, silica fume, and at least one blowing agent may be provided with a binder and processed in an industrial granulator. The method for preparing one or more expandable silica particles further includes the step of coating the outer surface of the expandable silica pre-particles with a coating comprising kaolin and talc, thereby forming expandable silica particles.
[0015] The method for producing expanded silica particles includes providing a plurality of expandable silica particles according to the present disclosure and heating the expandable silica particles in the chamber 2 of the furnace 1 to a temperature greater than the activation temperature of the blowing agent to form expanded silica particles. The expandable silica particles may be introduced into the chamber 2 through a feeding system ( Figure 1(shown schematically). In chamber 2, expandable silica particles can be fed onto an angled vibrating plate body. Direct high-frequency motion can thereby be induced in the expandable silica particles, where the motion can be chaotic or turbulent. Preferably, the expandable silica particles can first be fed into a preheating chamber before being fed or transferred into chamber 2. Advantageously, the temperature difference between the core and the surface of the expandable silica particles is minimized during preheating. In chamber 2, the expandable silica particles are heated to a temperature greater than the activation temperature of the blowing agent, to a temperature of 560 - 950 °C, preferably 850 - 900 °C. The expandable silica particles soften during heating. Above the activation temperature of the blowing agent, an exothermic reaction occurs, driving the expansion of the softened particles. Advantageously, the coating on the outer surface of the expandable silica particles insulates the outer surface during the exothermically driven expansion. Thereby, the expansion process is counteracted at the surface of the expanded silica particles, resulting in a denser outer surface of the expanded silica particles compared to uncoated particles and more closed pores.
[0016] Within chamber 2, the temperature and residence time can be controlled, thereby controlling the expansion rate of the expandable silica particles. The residence time can be controlled by controlling the transfer rate of the particles in chamber 2. Furnace 1 can also include a vibrating plate 3 that forms the bottom of chamber 2. The vibrating plate 3 is preferably inclined at an inclination angle relative to the horizontal direction from the inlet downward to the outlet of the furnace. The vibrating plate 3 is vibrated during the heating and expansion of the expandable silica particles, thereby inducing motion in the expandable silica particles. Advantageously, the contact time between the silica particles in furnace 1 is thereby limited, minimizing the risk of the particles adhering to each other and to the furnace.
[0017] Upon leaving furnace 1, the expanded silica particles can enter a cooling zone that includes one or more stages maintained at progressively decreasing temperatures. The expanded silica particles are preferably cooled to ambient temperature in the cooling zone, allowing for further processing of the expanded silica particles. Within the cooling zone, the temperature and residence time of each stage can be controlled, thereby controlling the cooling rate of the expanded silica particles. Advantageously, the internal tension within the expanded silica particles due to different cooling rates at the particle surface and within the particle can thereby be minimized. After cooling, the expanded silica particles can be coated with a sodium silicate solution (also known as water glass), preferably at a temperature of 0.1 - 200 °C. Advantageously, the sodium silicate solution also reduces the surface porosity of the expandable silica particles, thereby improving the fluid absorption resistance in the expanded silica particles.
[0018] The expanded silica particles according to the present disclosure preferably have a bulk density of 150 - 900 g / l. Preferably, the expanded silica particles have a spherical or near-spherical shape. The expanded silica particles can be used as fillers in concrete, stucco, gypsum, mortar, epoxy resin, polyurethane, acrylate, or a suitable organic binder, or artificial turf, or as fillers in water filtration cartridges. Advantageously, the expanded silica particles have a significantly reduced fluid absorption capacity and can absorb, for example, a negligible amount of concrete additives when used as fillers in concrete matrix materials.
[0019] Example 1
[0020] Expandable silica precursor particles are provided by sintering 95 wt% silica powder, 3 wt% SiC powder expander, and 2 wt% silica fume into a block at 710 °C. The silica powder contains recycled flat glass. The SiC powder has a particle diameter of 0.01 - 2 μm. Then, the sintered block is crushed into expandable precursor particles, and the expandable precursor particles are filtered according to the particle diameter. The expandable precursor particles are dry-coated with a coating containing kaolin powder and talc powder to form expandable silica particles. The expandable silica particles contain 91.2 wt% silica powder, 2.88 wt% SiC powder, 1.92 wt% silica fume, 2 wt% kaolin powder, and 2 wt% talc powder. The expandable silica particles are preheated at 680 °C for 300 s before heating to 870 °C for 36 s. Then, before starting to cool at 200 °C for 18 s, heating is continued at 865 °C for 45 s and at 860 °C for 45 s. The resulting expanded silica particles have a bulk density of 275 g / l (measured according to UNI EN 1097-6:2013, Appendix C) and a diameter of 2 - 8 mm (measured according to the sieving method of UNI EN 933-1:2012). The crush resistance of the expanded silica particles (measured according to UNI EN13055-1:2003, Appendix A, paragraph 4.10) is measured as 6.19 N / mm 2 The water absorption rate measured according to UNI EN 1097-6:2013 (absorption rate after 5 minutes in Appendix C) is 4.4%.
[0021] Comparative Example
[0022] Expandable silica precursor particles are provided by sintering a mixture of 97 wt% silica powder and 3 wt% SiC powder expander into a mass at 710 °C. The silica powder contains recycled flat glass. The SiC powder has a particle diameter of 0.01 - 2 μm. The sintered mass is then crushed into expandable precursor particles, and the expandable precursor particles are filtered according to particle diameter. The expandable precursor particles are then dry-coated with a coating containing kaolin powder to form expandable silica particles. The expandable silica particles contain 93.12 wt% silica powder, 2.88 wt% SiC expander, and 4 wt% kaolin coating. The expandable silica particles are heated and cooled in the same manner as in Example 1. The bulk density, particle diameter, water absorption, and crush resistance are measured according to the same criteria described in Example 1. The resulting expanded silica particles have a particle diameter of 2 - 8 mm, a bulk density of 300 g / l for the portion with a particle diameter of 2 - 4 mm, and a bulk density of 275 g / l for the portion with a particle diameter of 4 - 8 mm. The expanded silica particles have a water absorption of 24.2% for the portion with a particle diameter of 2 - 4 mm and 21.9% for the portion with a particle diameter of 4 - 8 mm. Finally, the expanded silica particles in the comparative example have a crush resistance of 3.5 N / mm for the portion with a particle diameter of 2 - 4 mm 2 and 2.7 N / mm for the portion with a particle diameter of 4 - 8 mm 2 .
Claims
1. A method for preparing one or more expandable silica precursor particles, comprising: (a) sintering or hot-pressing a mixture of silica powder, silica fume, and at least one blowing agent into a block at a temperature below the activation temperature of the at least one blowing agent, and dividing the block into expandable silica precursor particles; or (b) directly hot-pressing a mixture of silica powder, silica fume, and at least one blowing agent into expandable silica precursor particles; or (c) providing a mixture of silica powder, silica fume, at least one blowing agent, and a binder, and processing the mixture in a granulator.
2. The method according to claim 1, wherein the silica powder comprises recycled glass powder.
3. The method according to claim 1, wherein the at least one blowing agent comprises a powder including aluminum nitride, silicon carbide, manganese dioxide, sodium carbonate, calcium sodium carbonate, or a combination thereof.
4. The method according to claim 3, wherein the particle diameter of the blowing agent powder is 0.01 - 40 μm.
5. The method according to any one of claims 1 to 4, wherein the at least one blowing agent comprises silicon carbide powder.
6. The method according to claim 5, wherein the silica powder comprises recycled glass powder.
7. An expandable silica particle prepared by the method according to any one of claims 1 to 6.
8. The expandable silica particle according to claim 7, having a diameter of 0.1 - 40 mm.
9. The expandable silica particle according to claim 7 or 8, having a diameter of 0.25 - 5.6 mm.
10. A method for preparing expanded silica particles, comprising: (a) providing expandable silica precursor particles obtained by the method according to any one of claims 1 to 6; (b) providing a coating on the outer surface of the expandable silica precursor particles to form expandable silica particles, wherein the coating comprises kaolin powder and talc powder; and (c) heating the expandable silica particles in a chamber of a furnace to a temperature higher than the activation temperature of the blowing agent to form expanded silica particles.
11. The method according to claim 10, wherein the expandable silica particles in the chamber are heated to a temperature of 560 - 950 °C.
12. The method according to claim 10, wherein the expandable silica particles in the chamber are heated to a temperature of 850 - 950 °C.
13. The method according to any one of claims 10 to 12, wherein the expandable silica particles have a diameter of 0.1 - 40 mm.
14. The method according to any one of claims 10 to 12, wherein the expandable silica particles have a diameter of 0.25 - 5.6 mm.
15. An expanded silica particle prepared by the method according to any one of claims 10 to 14.
16. Use of the expanded silica particle according to claim 15 as a filler in concrete, stucco, gypsum, mortar, epoxy resin, polyurethane, acrylate, artificial turf, or as a filler in a water filtration filter element.